Urea is commonly used as a fertiliser, supplying nitrogen to plants. Urea granules are often friable, breaking into smaller particles and creating substantial amounts of dust during storage, transport and use.
U.S. Pat. No. 4,587,358 discloses that the physical properties of urea particles can be improved by incorporating formaldehyde, or, more desirably from a safety perspective, by incorporating a lignosulphonate such as calcium lignosulphonate. U.S. Pat. No. 4,676,821 discloses urea particles that contain calcium lignosulphonate and that additionally have a coating of elemental sulphur. The sulphur coating enables a controlled dissolution rate of the urea fertiliser.
The present inventors have sought to prepare a urea fertiliser having improved physical properties, in particular improved hardness.